Place the egg and milk in a small bowl and whisk with a fork. Place the ﬂour, baking powder, sugar and salt in a medium-sized bowl and whisk to combine. Mix the egg and milk into the ﬂour and stir until it is homogenous. Drain and squeeze the sultanas and grate the apple. Add these to the dough along with the zests and stir well to combine – the mixture should be thick but pourable. Add a bit of extra ﬂour if it is too liquid. Heat 4–5 cm (11/2–2 in) oil in a heavy-based saucepan (or use a deep-fryer) to 170°C (340°F) or until a cube of bread dropped into the oil sizzles in 5 seconds. Using two metal tablespoons dipped in the hot oil, pick up a ball of mixture with one spoon, and push it into the hot oil with the other spoon. The balls should be as big as an apricot. Don’t worry if you get little trails of dough. Cook 3–4 at a time, depending on the size of your pan, for about 4 minutes, until golden brown all over. Drain on kitchen towel and break open a fritola to check that it is cooked through. If it isn’t, reduce the temperature of your oil slightly and wait a minute or two. Once the fritole have cooled slightly, dust with icing sugar and serve warm.